With increasing demand for communication capacity, communication networks that use wavelength division multiplexing (WDM) technology are becoming increasingly widespread. With WDM technology a plurality of optical signals with different wavelengths are multiplexed and transmitted. A WDM apparatus using WDM technology is capable of transmitting a greater amount of data at a high speed compared with other transmission apparatuses.
An example of a transmission apparatus using WDM technology is an optical add-drop multiplexer such as a reconfigurable optical add-drop multiplexer (ROADM). The optical add-drop multiplexer includes an optical signal transmitting/receiving unit that may be called a transponder. The optical add-drop multiplexer multiplexes optical signals input from the transmitting/receiving unit and transmits the resultant multiplexed optical signal elsewhere. Conversely, when a multiplexed signal is received from elsewhere, the optical add-drop multiplexer extracts a signal that has a particular wavelength and outputs the resultant signal to the transmitting/receiving unit.
The optical add-drop multiplexer includes an optical cross-connect apparatus that includes both an optical amplifier and a wavelength selective switch disposed for each line such that multiplexed signals are allowed to be transmitted along different lines. Note that in the embodiments discussed here, a line refers to a transmission line extending from an optical cross-connect apparatus to a node with which a connection for communication is or may be established.
The optical amplifiers and the wavelength selective switches are connected via optical fibers. The number of optical fibers used in an optical add-drop multiplexer (for example, several hundred) is greater than other types of transmission apparatuses, and thus misconnections of optical fibers may be more likely to occur.
To deal with misconnected optical fibers, for example, Japanese Laid-open Patent Publication No. 2005-51750 discloses a technique of detecting and correcting a misconnected optical fiber with reference to a transmitting port and a receiving port between transmission apparatuses. Japanese Laid-open Patent Publication No. 2004-32088 discloses a technique of detecting a misconnected optical fiber by comparing the optical power level at the stage preceding a multiplexer apparatus, which is configured to multiplex a plurality of wavelength signals, with the optical power level at the stage following the multiplexer apparatus.